Such choke valves are comparable with known starter valves which shut off the entry of the main air into the carburetor so as to produce an especially rich mixture in the carburetor when a cold engine is being started. When the piston descends in the cylinder of the engine, a very strong pumping action is then produced in the carburetor, so that the high vacuum will draw large amounts of fuel both from the mixer tube and from the idler system of the carburetor. Such starter valves or choke valves can be operated either by hand (with a choke lever) or automatically (with an automatic choke).
At the present time it is known that the maximum engine speed can be attained by enriching the fuel in the air-fuel mixture. However, establishing the maximum engine speed by enriching the mixture is comparatively inaccurate. The engine speed is therefore set at about 14,000 rpm, even though the engine has its maximum power at about 9,000 rpm. At 14,000 rpm, limiting the speed by reducing the fuel feed can easily lead to the destruction of the engine. Another undesirable aspect of known carburetor operation is that at maximum engine speed, which is achieved by enriching the fuel in the air-fuel mixture, a very great amount of unburned fuel is exhausted. The adverse effect of this on efficiency is obvious, and it also results in an extraordinary discharge of toxic substances, resulting in pollution of the environment.